1. Field of the Invention
The invention relates to a transmission system comprising a plurality of network nodes which are provided each for receiving and transmitting packets which contain connection-related status information signals about the transmission system.
2. Discussion of the Related Art
Such a transmission system comprising a plurality of network nodes is known from the title "ATM--Die Technik des Breitband-ISDN" by Gert Sigmund, R v. Decker's Verlag, G. Schenck, Heidelberg, 1993, pp. 133 to 137. Such network nodes may be, for example, switching centres, cross-connects or regenerative repeaters. Data or information signals are then transmitted between the network nodes in fixed-length packets (cells) in the asynchronous transfer mode. The packets or cells may then be transported in a synchronous transport module (STM) which forms part of a signal according to the standard of the synchronous digital hierarchy (SDH) or according to the standard of the synchronous optical network (SONET). A cell consists of a 5-byte-long header field which contains control information, and a 48-byte-long information field. The control information in the header field of a cell contains a Virtual Path Identifier (VPI) which indicates a virtual path (VP), and a Virtual Connection Identifier (VCI) within a virtual path, which indicates a Virtual Connection (VC). A plurality of VCs are combined to become a virtual path.
To ensure proper operation, to ensure that error conditions are signalled and monitor information signals (for example, with respect to the availability and efficiency of the system) are transported, cells carrying OAM data (OAM cells) in their information field are exchanged between the network nodes (OAM=Operations Administration and Maintenance). How such OAM cells are evaluated in a network node is not known from above title.